Home Secretary Priti Patel has been defended by allies over claims that she bullied officials.
She is reported to have clashed with the senior mandarin at the Home Office and has been accused of belittling officials, making unreasonable demands and creating an “atmosphere of fear”.
Business minister Nadhim Zahawi rejected the allegations, insisting Ms Patel was “utterly professional” and “works day and night”.
The Home Office said no formal complaints had been made against the Cabinet minister.
According to The Times, Ms Patel has sought to oust permanent secretary Sir Philip Rutnam from the Home Office, and he has raised concerns with the Cabinet Office about the minister.
The newspaper said matters came to a head last week when a senior official collapsed after a meeting with Ms Patel following an all-night effort to reverse a High Court ruling barring the deportation of 25 foreign criminals to Jamaica.
At a meeting the following morning he was confronted by the Home Secretary, who demanded to know why the department had failed to reverse the ruling.
He reportedly fell ill later during another meeting and was taken to hospital, where he was found to have a sodium deficiency.
Mr Zahawi told LBC: “I’ve known Priti for 25 years, she’s utterly professional, works night and day to deliver for the country and her constituents and is absolutely focused on making sure… the people voted for us to take back control of our borders.”
Pushed again on whether Ms Patel is a bully, Mr Zahawi said: “No, I don’t think she is at all.
“I’ve worked with Priti in the past on several campaigns, I’ve known her literally for 25 years, she is a brilliant, collegiate team player.”
But Dave Penman, general secretary of the FDA union which represents senior civil servants, said staff at the Home Office were “working flat out” and warned that ministers must recognise the consequences of their behaviour.
He said: “The Home Office, by its very nature, has a wide-reaching, demanding policy agenda, and civil servants working in the department are used to rising to these challenges.
“Members in the Home Office are already working flat out, with our latest survey finding 70% within the department felt the working of excess hours is a problem, with the same amount stating they had worked whilst on sick leave in the last year.
“Putting undue pressure and demands on committed public servants that are already overstretched does not make for good government and will do this administration no favours in delivering its policy priorities.
“Ministers have to recognise the consequences of their behaviour. An ‘atmosphere of fear’ is obviously not conducive to a successful workplace and anonymous briefings against civil servants who cannot answer back are not only unfair to the individual, they corrode public trust in government.”
A Home Office spokesman said: “We have not received any formal complaints and we take the welfare of our staff extremely seriously.”
An ally of Ms Patel told The Times: “The Home Office is dysfunctional and the current permanent secretary had presided over a sacking of a home secretary (Amber Rudd) and accidental deportations.
“If this were any other environment Philip Rutnam would not only be sacked he’d be denied a pension.”
But a Home Office source told the newspaper: “Sir Philip and (she) have fundamental disagreements about the rule of law. He’s committed and she isn’t.
“She’s belittled him and caused consternation, and she frequently encourages behaviour outside the rule of law.”